1. Field of the Invention
This invention concerns a magnetoresistive head and initialization method therefor, and more particularly concerns a magnetoresistive head in which the giant magnetoresistivity (GMR) effect is utilized, and an initialization method therefor.
2. Description of the Related Art
MR heads wherein the magnetoresistivity effect is employed exhibit high magnetic-field responsiveness and sensitivity, and hence are used in high-density magnetic recording apparatuses. In conventional MR heads, magnetic films are used which exhibit an anisotropic magnetoresistivity (AMR) effect for the magnetoresistive material. In such an AMR-type MR head, the electrical resistance is proportional to the current supplied to the magnetoresistive material and to the square of the cosine of the angle at which the magnetoresistive material magnetizes. In a magnetic recording apparatus, the magnetic field of the signal from the magnetic recording medium changes the direction of magnetization in the magnetoresistive material. This change, in turn, induces changes in the resistance value of the magnetoresistive material and in the currents and voltages sensed. Thus it is possible to read recorded data from the magnetic recording medium.
Recently, the giant magnetoresistivity (GMR) effect has been discovered in materials that exhibit even greater magnetoresistivity. The essential characteristic of these materials is that at least two ferromagnetic metal layers are separated by a non-ferromagnetic metal layer. This GMR effect is observed in Fe/Cr or Co/Cu multilayer film systems which exhibit strong anti-ferromagnetic coupling in the ferromagnetic layers, and in systems wherein the direction of magnetization is fixed or pinned in one of two ferromagnetic metal layers. In the GMR effect, the electrical resistance is proportional to the cosine of the angle subtended by the magnetism in adjacent ferromagnetic layers, and is independent of the current direction.
A magnetic head in which such a GMR effect is employed is disclosed in Laid-Open Patent Application H4-358310 [1992] (in gazette). FIG. 5 is a cross-sectional diagram of one example of a conventional magnetic head wherein the GMR effect is used. A magneto-sensitive portion that senses signal fields comprises a first ferromagnetic layer 1 and a second ferromagnetic layer 3 separated by a non-magnetic metal layer 2, and an anti-ferromagnetic layer 4 for pinning the magnetism of the second ferromagnetic layer by exchange coupling. The magnetization in the first ferromagnetic layer 1 that is unpinned and free is established so as to be perpendicular to the magnetization in the second ferromagnetic layer 2 that is pinned. When the magnetization of the pinned second ferromagnetic layer 3 is parallel to the direction of the signal field 22, and the magnetization of the free first ferromagnetic layer 1 is perpendicular to the signal field 22, the linear response is the greatest, and the dynamic range is the widest. At such times, only the magnetization in the first ferromagnetic layer 1 turns freely, the angle between the two-layer magnetization changes, and this is sensed as a change in resistance. Also, as means for creating a vertical bias field to hold the first magnetic layer in a single domain state, an anti-ferromagnetic layer 8 is provided adjacent to the edges of the first ferromagnetic layer.
Thus, in conventional magnetic heads using the GMR effect, the direction of pinning the second ferromagnetic layer differs from the vertical bias direction. Here, in order to pin the ferromagnetic layer using an anti-ferromagnetic layer, a film must be formed wherein a ferromagnetic layer is in contact with an anti-ferromagnetic layer, and this must be heated to near the blocking temperature of the anti-ferromagnetic layer in a magnetic field. When that is done, the two anti-ferromagnetic layers must have sufficiently different blocking temperatures. The reason for this is that, when the blocking temperatures are similar, between the process of heating in a magnetic field to perform pinning on the second ferromagnetic layer and the process of heating in a magnetic field to pin the vertical bias direction, only the pinning direction in the process performed later than the other will be effective. For this reason, there is a troublesome aspect in that the two anti-ferromagnetic layers must be formed of materials having sufficiently different blocking temperatures.